Lady Gaga's security team roughed up a fan who tried to snag her picture during the superstar's party at the Top of the Standard Monday night.

Gaga, who was honored with the Fashion Icon Award at the Council of Fashion Designers of America awards gala, threw an after-party at the Standard Hotel with V magazine editor Stephen Gan and designer Nicola Formichetti.

She was serenaded by soul legend Patti LaBelle, who sang "Somewhere Over the Rainbow" in front of Gerard Butler, Karolina Kurkova, Prabal Gurung, Liv Tyler,Gaga's parents and her ex Luc Carl, with whom she seemed friendly all evening.

Later during the night, sources said Gaga was coming downstairs from the roof to The Top when a fan took a picture of her with his phone.

A spy told us, "One of her over-protective security guards started roughing him up. He pushed the guy up the stairs, grabbed his phone and threw it, then dragged him back up onto the roof."

Upon seeing the scuffle, our spy said, Gaga told her guard, "What are you doing? Leave him alone." The source added that Gaga, "looked embarrassed and shook her head." A Gaga rep didn't get back to us and an event rep had no comment.

Meanwhile, one guest fell in the pool in his tuxedo, and by 3 a.m. Nicky Hilton was "looking totally wasted," a witness said. "She was dancing like crazy, stumbling and twirling around, and tried to drag [Theory designer] Olivier Theyskens over to dance with her. Olivier pretended to dance, then he blew her off and returned to his friends."

Hilton "kept putting her clutch purse down and forgetting where she'd left it, then getting angry thinking somebody had taken it," the source added. She was also spotted "crawling around on the floor looking for something" at about 4 a.m.

A rep for Hilton said, "These events have been exaggerated. Nicky panicked when she misplaced her purse, but thankfully found it." Despite the antics, a grateful Gaga was in tears after LaBelle's performance, telling Gan, "All you need to do now to top this is to bring Luther Vandross [back]."